Most of the places I go, public campgrounds with back in sites, the site length is the length of the site. They are not thinking about what you are going to put into it, as there are all kinds of combinations of RVs, cars, trucks, boat trailers. Some people won't even be coming with a RV, but may need to park two cars and a boat trailer in the site where they put up their tents.
So if you come with a 25 foot towable, and take a 25 foot site, you can expect that what you used to tow it may not fit. One of the situations I often find is that the shorter parking sites are wide enough for two vehicles, particularly toward the entrance.
Tom Test
Itasca Spirit 29B